Lumbriculus ambiguus was described by Holmquist in 1976, based on material collected in northern Alaska. Like L. genitosetosus

Lumbriculus genitosetosus

Lumbriculus genitosetosus was described by Holmquist in 1976 from almost 2,000 individuals collected in Northern Alaska. Initially, Holmquist revived the genus Thinodrilus for L...

, L. ambiguus was initially placed in the genus Thinodrilus along with L. inconstans, but this genus is generally not recognised today. Its genital characters vary greatly between individuals, but certain features (such as the location of the atria in segment VIII) appear to be constant.